There has been considerable attention on using multicarrier communication techniques to transmit information over wireless channels. For example, orthogonal frequency division multiplexing (OFDM) has been picked as the basis for the 802.11a and 802.11g standards for wireless local area networks.
Multicarrier systems have several features which make them attractive to the wireless medium. For one thing, the equalization task in a well designed system can be simply implemented as a multiplication on each subcarrier rather than via a RAKE-receiver scheme or a convolution. Moreover, estimating the parameters required for receiver processing is reliably done with a simple algorithm since the signals are disjoint and narrow band, each experiencing a simple flat fading.
The multicarrier system can also be set up so that some or all the users have orthogonal waveforms. Multicarrier systems can conceptually maximize the information capacity of the network by careful allocation of power and bit rate among its subcarriers.
However, the multicarrier systems present significant challenges to the system designer. Several schemes have been proposed to meet these challenges, many of which use pilots or training sequences.
Conventional methods of wireless “multiple access” communication have difficulty with interference when many devices are assigned to a single wireless network, as well as when another network of wireless devices exists nearby at the same frequency. When there is interference, such conventional systems may begin to output a higher bit error rate (BER) and, may possibly fail to operate reliably, thus dropping devices and connections in a seemingly random fashion.
Tree structured interference is known to allow for an overpacking of the available channel resources, while allowing for an optimal multiuser joint detector to be implemented in real-time. In contrast, optimal joint detection for interfering (non-orthogonal) users in a multiple access communication system generally has a computational complexity that increases exponentially with the number of users. Thus, practical limitations necessitate the integration of tree structured techniques into multiple access systems such as wireless local area networks, mobile and cellular terrestrial systems, and satellite-based systems.
There is a need, therefore, for techniques that alleviate degraded performance and throughput in a wireless communication system due to interference from other transmitters in the system assigned to either the same network or to a different nearby network.